1. Field of the Invention
The present invention relates to a method of manufacturing rice which abundantly contains gamma aminobutyric acid in an endosperm part.
2. Description of Related Art
Conventionally, it is said that effects of preventing hypertension and improving blood flow can be obtained by taking gamma aminobutyric acid. Therefore, germinated brown rice and germinated soybean which are foods with an increased content of the gamma aminobutyric acid are generally manufactured. Seeds of rice, soybean, and the like are germinated so that nutrition including gamma aminobutyric acid and vitamin B group is enriched without using additives more than usual.
In the conventional method of manufacturing germinated brown rice, in general, brown rice with embryo is put into a soak tank or the like with water and a water temperature in the soak tank is kept to be substantially 25 to 35° C. by using an electric heater or the like. Then, the brown rice is soaked in the water in the soak tank for 24 to 72 hours so as to be germinated. The brown rice soaked in the water absorbs water and a moisture content of the brown rice is increased. Further, the brown rice is heat-retained at a temperature suitable to germination. Eventually, the brown rice starts to germinate and becomes in a so-called “pigeon breast state”. In the pigeon breast state, the embryo grows to a size of substantially 0.5 mm to 2.0 mm so that germination can be observed seemingly. The germinated brown rice obtained in such a manner contains gamma aminobutyric acid abundantly in comparison with that contained in usual brown rice. Brown rice contains only 2 to 3 mg/100 g of gamma aminobutyric acid and polished rice contains only substantially 1 mg/100 g of gamma aminobutyric acid. On the other hand, a content of gamma aminobutyric acid in the germinated brown rice is increased to substantially 5 to 20 mg/100 g.
Further, a technique of manufacturing germinated rice with embryo buds obtained by polishing germinated brown rice while embryo is left and removing bran layer has been commonly known by applying the above technique of manufacturing germinated brown rice (see Patent Document 1). Flavor of the germinated rice with embryo buds is improved in comparison with that of the germinated brown rice by removing the bran layer therefrom.    [Patent Document 1] Japanese Patent Application Laid-open No. 2005-333829
However, in the conventional germinated brown rice and germinated rice with embryo buds, gamma aminobutyric acid is increased in embryo and bran layer. Therefore, if the germinated brown rice or the germinated rice with embryo buds is polished to obtain polished rice, there arises a problem that a content of the gamma aminobutyric acid in the obtained polished rice is decreased to an equivalent level to that of usual polished rice. Therefore, the germinated brown rice or the germinated rice with embryo buds is cooked while embryo and bran layer are left so that the flavor of the germinated brown rice or the germinated rice with embryo buds is poorer than that of polished rice. The flavor thereof can be improved by mixing the germinated brown rice or the germinated rice with embryo buds with usual polished rice and cooking. However, the following problem arises in this case. That is, if the germinated brown rice or the germinated rice with embryo buds which abundantly contains gamma aminobutyric acid is mixed with the polished rice which is poor in gamma aminobutyric acid, a content of the gamma aminobutyric acid by weight in cooked rice is largely decreased.
Further, if brown rice is soaked for a long period of time in order to germinate the brown rice, when the brown rice is dried after being soaked, there arises a problem that so-called “cracking” is easily caused. The cracking is a phenomenon that a surface of brown rice is cracked. The flavor of the cracked rice is bad because a grain of the rice is cracked when polished or texture of the rice becomes sticky when boiled. Further, since bacteria is easily developed in water at a temperature suitable to germination of brown rice, there is a risk that an unusual odor is caused in the brown rice when soaked in the water and the flavor thereof is further deteriorated.